OP0020 THE CELLULAR METABOLISM OF SLE NK CELLS IS PRIMARILY ALTERED AT THE LEVEL OF MITOCHONDRIAL HOMEOSTASIS
Authors: N. Fluder, M. Humbel, C. Ribi, D. Comte
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Systemic lupus erythematosus (SLE) is a multi-systemic inflammatory disease, of unknown etiology, which involves the development of autoreactive cells and a loss of tolerance to self. Natural Killer (NK) cells represent a group of innate immune cells that play a pivotal role in the interaction between the innate and adaptive immune system. In patients with SLE, NK cells are decreased in the peripheral blood, exhibit reduced cytotoxicity, and impaired cytokine production.(1, 2) To date, few studies have explored the molecular mechanisms underlying NK cell dysfunction in SLE. <h3>Objectives</h3> To characterize the immunometabolic alterations of NK cells from patients with SLE. <h3>Methods</h3> SLE and healthy NK cells were isolated from human PBMCs. Glycolysis and mitochondrial respiration (OXPHOS) were measured using Seahorse real-time metabolic assay. Mitochondrial function (membrane potential, mitochondrial mass), superoxide levels and lysosomes acidification were assessed by flow cytometry. Mitochondrial membrane potential and mass were analyzed by confocal microscopy (CM). Mitochondrial DNA was quantified by qPCR. Mitochondrial structure was examined by transmission electron microscopy (EM). Functional (cytokine production, degranulation) assays were performed in parallel with mitochondrial mass measurement by flow cytometry. Quantitative proteomic analysis was conducted focusing on the expression of proteins involved in mitochondrial homeostasis. <h3>Results</h3> We first examined the cellular metabolism of SLE NK cells in comparison to healthy NK cells. We observed that OXPHOS is significantly increased in SLE NK cells, while glycolysis is similar to healthy controls. Due to this alteration in oxidative phosphorylation, we conducted experiments to examine the mitochondrial fitness of SLE NK cells. We showed that mitochondrial mass is increased, while mitochondrial activity is decreased in SLE NK cells, suggesting an accumulation of dysfunctional mitochondria. SLE NK cell mitochondria displayed increased superoxide levels and elevated lysosomal acidification, compared to healthy NK cells. qPCR analysis showed no significant difference.in mitochondrial DNA between SLE NK cells and healthy controls suggesting that the size of mitochondria is increased but not their number in SLE NK cells. Examination of the mitochondrial structure in SLE NK cells by TEM, showed cristae disorganization. Quantitative proteomic analysis showed that SLE NK cells express high levels of proteins associated with mitochondrial synthesis (mitochondrial import receptor TOM6) and OXPHOS (ATP synthase F(0), NADH deshydrogenase1 C1). In parallel, we observed a reduction in proteins key for mitochondrial clearance such as E3 ubiquitin ligases (RNF181, MARCHF5), as well as lysosomal acidification (Proton-transporting V-Type ATPase), in SLE NK cells. <h3>Conclusion</h3> SLE NK cells exhibit impaired mitochondrial respiration, which is linked to an accumulation of large mitochondria with cristae disorganization. These results suggest an alteration in mitochondrial degradation in SLE NK cells related to dysfunctional mitophagy. Taken together, these data suggest that impaired mitochondrial function and homeostasis represent a major feature of SLE pathogenesis. <h3>References</h3> [1] Spada R, Rojas JM, Barber DF. Recent findings on the role of natural killer cells in the pathogenesis of systemic lupus erythematosus. J Leukoc Biol. 2015;98(4):479-87. [2] Park Y-W, Kee S-J, Cho Y-N, Lee E-H, Lee H-Y, Kim E-M, et al. Impaired differentiation and cytotoxicity of natural killer cells in systemic lupus erythematosus. Arthritis &amp; Rheumatism. 2009;60(6):1753-63. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.